Lost Foam Casting Process

History of Lost Foam for Metal Casting

The lost foam casting process originated in 1958 when H.F. Shroyer was granted a patent for the cavity-less method, using a polystyrene foam pattern imbedded in traditional green sand. The polystyrene foam pattern left in the sand is decomposed by molten metal. The molten metal replaces the foam pattern and precisely duplicates all of the features of the pattern.

The Casting Process

A pattern is made from molded polystyrene foam. The final pattern is approximately 97.5% air 2.5% polystyrene.

The foam is coated with ceramic investment, also known as refractory coating, by dipping, brushing, spraying, or flow coating. The coating creates a barrier between the smooth foam surface and the coarse sand surface. The coating also controls permeability, which allows the gas created by the vaporized foam pattern to escape through the coating into the sand. The coating forms a barrier so that the molten metal does not penetrate and cause sand erosion during pouring.

After the coating dries, the cluster is placed into a flask and backed up with un-bonded sand. The sand is then compacted using a vibration table. Once compacted the mold is ready to be poured.

Molten metal is poured into the polystyrene pattern, which vaporizes and is replaced by metal. Vents in the side of the flask allow vapor to escape.